The present invention is directed to a method and apparatus for a calcining and sintering lumpy materials, such as limestone, dolomite or the like, in a substantially vertical shaft kiln in which the materials are passed in succession through a pre-heating zone, a calcining zone, which has both an upper and lower range, and a cooling zone. In this invention, an annular chamber, which received the material to be processed, is formed by a circumferential wall of the kiln and a cylindrical shaft insert which are spaced apart by refractory bridges which extends therebetween. Cooling air is introduced into the bottom of the cooling zone to flow upward towards the calcining zone. Each of the upper and lower ranges of the calcining zone have burner units or arrangements for introducing fuel and air for burning to produce combustion gases or products with the combustion gases of the upper zone flowing upward towards the preheated zone and the combustion gases in the lower range flowing both upward and downward. The cylindrical shaft insert is provided with an arrangement for removing the cooling air and the combustion gases which are flowing downward towards the cooling zone and then adding additional air and directing this with fuel to the burner units associated with the lower range of the calcining zone. By controlling the amount of the air and the amoung of fuel, different ratios can be obtained so that an excess of air or a deficiency of air can be obtained as well as different temperatures can be obtained in the upper calcining range and the lower calcining range.
A method as well as a ring shaft kiln, which enables passing material through a preheating zone, an upper range and a lower range of a calcining zone and finally into a cooling zone, is known from German Letters Patent No. 1,281,111. In the device of the German Patent, the circulation of gases is employed in the lower part of the lower range of the calcining zone and the fuel is separately supplied to the air flowing through the upper range of the calcining zone in such a manner that a slightly excess amount of air and a high temperature is developed in the upper range of the calcining zone for an intensive deacidification of the material while a high air excess with a low temperature is provided in the lower range of the calcining zone for the remaining deacidification.
Given such kilns, the manner in which the fuel is introduced is of a great importance. For example, fine grained or lumpy, solid fuel can be directly introduced into the interstitial volume of the bulk of the material to be processed and preferably is introduced at a plurality of locations on the kiln wall. The interstitial volume will be formed by the hollow spaces that occur between the material being processed which is a lumpy material. Depending upon the type of material, these hollow spaces have a great range of different sizes and shapes. Beyond that, it must be taken into consideration that the material is moved through the kiln so that the outflow conditions at the discharge of the delivery elements constantly changes during the operation. When given such an introduction of the fuel into the interstitial volume of the bulk material and since the size of the hollow spaces in the bulk material are comparable to the outflow cross-section of the fuel, stable and controlled introduction conditions for the fuel cannot be achieved.